The present invention relates generally to fasteners and more particularly to insert fasteners adapted for securement within an opening in a panel by a threaded member.
Insert fasteners are well known in the art and are commonly used in the automotive industry to secure objects, such as interior trim, onto a panel, such as an automotive body panel.
Insert fasteners are used to secure interior and exterior trim onto an automotive panel in the following manner. Specifically, the insert fastener is typically pushed into a square-shaped opening which is punched, molded or formed in an automotive panel, the body panel being typically manufactured out of a soft sheet metal or plastic. With the insert fastener disposed within the opening, the interior trim is positioned against the automotive body panel. A threaded member, such as a screw, is then driven through the interior trim and into threaded engagement with the insert fastener, thereby securing the trim onto the automotive body panel. In the automotive manufacturing process, the threaded member is commonly driven through the trim and into the insert fastener using automatic screw driving devices which have torque levels of approximately 5 Newton-meters.
One type of insert fastener which is well known in the art is the snap-in insert fastener.
Snap-in insert fasteners, also commonly referred to as snap-in fasteners, typically comprise one or more resilient fingers which are adapted to flatten as the fingers are pressed into the aperture in the automotive body panel. Once the fingers pass through the aperture and onto the opposite side of the body panel, the fingers outwardly snap back to their original configuration to lockingly secure the fastener onto the automotive body panel.
Snap-in fasteners of the type described above are often constructed out of a solid, molded plastic which includes a central bore therethrough. In use, self-threading screws are typically driven in the central bore and into threaded engagement with the fastener.
As an example of a snap-in fastener, in U.S. Pat. No. 5,593,263 to J. P. Clinch et al, there is disclosed a snap-in fastener that is adapted to having an object such as automobile trim secured thereto by a threaded member such as a screw. The snap-in fastener features a pair of opposed resilient fingers having a contoured cross-section which enable them to flatten as they are pressed into an aperture in a panel. The fingers flatten as they are pressed into the panel aperture until free-ends of tabs extending therefrom spring or snaps outwardly to engage the opposite side of the panel to lockingly secure the fastener and the trim to the panel while enabling the fingers to resume their original contoured cross-sectional configuration.
Although well known and widely used in commerce, snap-in insert fasteners experience some notable drawbacks.
As a first drawback, snap-in insert fasteners require an extremely high level of force in order to remove the fastener from the panel. Consequently, snap-in insert fasteners are effectively incapable of being backed out of the opening in the panel without destroying the shape of the aperture in the panel. Because snap-in fasteners can not be backed out of the aperture in the body panel, the fasteners are rendered incapable of reuse or replacement. This is particularly significant with regards to snap-in fasteners that are constructed of plastic. Specifically, it has been found that automatic screw driving guns, which are routinely used on the assembly lines of automobile manufacturers, drive the threaded member into the fastener at such a high torque (approximately 5 Newton-meters) that the plastic fastener becomes stripped as the threaded member is driven through the central bore. As a result, the stripped plastic fastener is unable to hold the screw, thereby rendering the plastic fastener useless. Because the stripped plastic fastener is incapable of being backed out of the door panel, the fastener has to be knocked into and through the door panel aperture in order to remove the stripped plastic fastener. By knocking the plastic fastener into the door panel, the insert is irretrievably lost within the door panel interior. Positioned free within the door panel interior, the insert tends to bounce around and rattle within the door panel, thereby creating unwanted noise.
As a second drawback, it has been found that the tight, snap-fit securement of snap-in insert fasteners within an associated opening in the body panel limits the range of potential applications in which the fastener can be used. In particular, the snap-fit mechanics of a snap-in insert fastener allows for the fastener to be used only in conjunction with body panels having apertures of limited sizes and in conjunction with body panels of limited thicknesses.
As a third drawback, it has been found that snap-in insert fasteners require a relatively high insertion force (approximately 10 pounds) in order to push the fastener into the opening in the automotive body panel. As a result, the entire manufacturing process of securing the interior trim onto the body panel is rendered more difficult and time consuming.
Another type of insert fastener which is well known in the art is the expansion insert fastener.
Expansion insert fasteners, also commonly referred to as expansion fasteners, typically comprise a pair of resilient legs and a central bore which is adapted to receive a threaded member. With the expansion fastener pressed into an aperture in an automotive body panel, the threaded member is driven into the bore of the expansion fastener until the threaded member spreads the pair of resilient legs apart and into engagement against the automotive body panel, thereby securing the fastener within the opening in the panel.
As an example of an expansion fastener, in U.S. Pat. No. 5,873,690 to M. R. Danby et al, there is disclosed a thread nut expansion fastener for securement within an opening to a panel by a threaded member. When the threaded member is rotationally advanced through a barrel nut, the threaded member causes the free-ends of resilient legs to move away from each other and engage and urge resilient fingers into contacting engagement with opposite sides of the opening with sufficient force to secure the fastener to the panel.
Although well known and widely used in commerce, expansion fasteners experience some notable drawbacks. For example, it has been found that the complex bending arrangement of the legs of expansion fasteners renders the manufacturing of expansion fasteners a relatively complicated and expensive process.